Search Results (2)

CO₂ geological sequestration in marine sediment is one of the important ways to lower carbon emissions. To study the influence of CO₂ sequestration on the permeability and porosity of unconsolidated strata, this paper conducted overpressure permeability, isothermal adsorption and CO₂ displacement experiments. Through nuclear magnetic resonance (NMR) technology, the effects of supercritical CO₂ (SCO₂) at different temperatures on the permeability evolution and pore size variation of unstratified strata in marine hydrate reservoirs were studied. The experimental results show that: (1) When the pressure changed from 0 to 17.5 MPa, the permeability and porosity of the soil samples decreased sharply. The porosity dropped from 36.83% to 16.07%, and the permeability also decreased from 48.53 mD to 1.18 mD. (2) During the adsorption tests, the fitted absolute adsorption capacity of CO₂ and CH₄ gradually increased with pressure growth. The maximum fitted absolute adsorption capacity of CO₂ was 2.45 times that of CH₄. (3) Through displacement experiments, the porosity and permeability increments during SCO₂ displacement were much greater than those during non-SCO₂ displacement. From 30 °C to 70 °C, the increments of porosity and permeability all increased. After SCO₂ displacement, the pores’ proportions (>0.1 μm) increased for all samples, with the largest growth rate reaching 34.37%. Above all, these results indicate that environmental pressure significantly affects the permeability of soil samples, and that SCO₂ displacement can effectively enhance the proportion of large-sized pores, thereby further improving the permeability of unconsolidated strata. Full article

Recently, shallow gas fields and hydrate-bearing sand in the deepwater area of the northern South China Sea have been successively discovered, and the accurate prediction of shallow sands is an important foundation. However, most of the current prediction methods are mainly for deep oil and gas reservoirs. Compared with those reservoirs with high degree of consolidation, shallow sandy reservoirs are loose and unconsolidated, whose geophysical characteristics are not well understood. This paper analyzes the logging data of shallow sandy reservoirs recovered in the South China Sea recently, which show that the sand content has a significant influence on Young’s modulus and Poisson’s ratio of the sediments. Therefore, this paper firstly constructs a new petrophysical model of unconsolidated strata targeting sandy content and qualitatively links the mineral composition and the elastic parameters of the shallow marine sediments and defines a new indicator for sandy content: the modified brittleness index (MBI). The effectiveness of MBI in predicting sandy content is then verified by measured well data. Based on pre-stack seismic inversion, the MBI is then inverted, which will identify the sandy deposits. The method proposed provides technical support for the subsequent shallow gas and hydrate exploration in the South China Sea. Full article